This invention relates to apparatus for providing information for use in determining the ink requirements of a printing cylinder. More particularly, the invention is directed to a system for analyzing a member such as a photographic film bearing an image to be printed by the cylinder and providing information as to the image area.
In offset printing, the thickness of a film of ink applied to a printing cylinder is controlled by regulating the quantity of ink in each of a plurality of adjacent columns along the surface of the cylinder. The quantity of ink in each column is controlled by a deformable metal blade which is positioned at each column closer to or farther from an inking roller by means of ink keys such as screws or other regulating means for each column. In some cases, each column may be supplied with ink by a piston pump which is controlled to vary the amount of ink supplied to the column. The amount of ink supplied may be adjusted by observing the printed product to determine in which columns there is too much or not enough ink and adjusting the ink keys, such as the positions of the screws, accordingly. An initial adjustment may be made by observing the image area to be printed in each column and adjusting the ink key for that column accordingly.
In U.S. Pat. No. 3,853,409 there is disclosed a system for obtaining information on the ink requirements of a printing cylinder by determining the amount of light transmitted through a photographic film of the image to be printed at each column thereof. The film may be either a positive or negative of the image to be printed. The surface to be printed is directly proportional to the dark area of the film for a positive or to the clar area for a negative. The film to be analyzed is placed between a stationary light source and a battery of photoelectric cells, one cell of large size for each column to be analyzed. The output information from the various cells may be viewed on a CRT to develop the initial ink key setting and/or may be recorded in digital form.
Although the system disclosed in U.S. Pat. No. 3,853,409 provides significant advantages over prior means for obtaining information for initial ink key settings, it requires a significant amount of manual intervention.
In U.S. Pat. No. 3,958,509 there is disclosed a system for determining initial ink key settings of a printing press in which a printing plate is imaged onto an electronic camera tube and scanned. The system requires access to the printing plate and is inconvenient for that reason.